Fine spinel-type ferrimagnetic particles containing Fe-Co-Ni and process for producing the same

Abstract

Fine spinel-type ferrimagnetic particles of the present invention have a composition represented by the formula (I):wherein 2.0<n=Fe/(Co+Ni)<3.0, 0.4<=x<=0.9, 0.1<=y<=0.6 and x+y=1. The fine spinel-type ferrimagnetic particles exhibit a high coercive force in spite of fine particles.

What is claimed is:  
     
       1. Fine spinel-type ferrimagnetic particles having a composition represented by the formula (I): 
       
         
           (CoO) x (NiO) y .n/2Fe 2 O 3    
         
       
       wherein 2.0<n<3.0, 0.4≦x≦0.9, 0.1≦y≦0/6, and x+y=1, and n=Fe/(Co+Ni).  
     
     
       2. Fine spinel-type ferrimagnetic particles according to  claim 1 , wherein n is from not less than 2.25 to less than <3.0. 
     
     
       3. Fine spinel-type ferrimagnetic particles according to  claim 1 , wherein n is 2.25 to 2.75. 
     
     
       4. Fine spinel-type ferrimagnetic particles according to  claim 1 , wherein x is 0.5 and y is 0.5. 
     
     
       5. Fine spinel-type ferrimagnetic particles according to  claim 1 , wherein y is 0.4 to 0.1. 
     
     
       6. Fine spinel-type ferrimagnetic particles according to  claim 1 , which comprise single-phase structure, and have a particle diameter of 10 to 50 nm, a saturation magnetization σs of 50.3×10 −6  to 88.0×10 −6  Wb.m/kg and a coercive force HcJ of 239 to 637 kA/m. 
     
     
       7. Fine spinel-type ferrimagnetic particles according to  claim 5 , wherein the particle diameter is 20 to 40 nm. 
     
     
       8. Fine spinel-type ferrimagnetic particles according to  claim 5 , wherein the coercive force HcJ is 279 to 637 kA/m. 
     
     
       9. Fine spinel-type ferrimagnetic particles having a composition represented by the formula (I): 
       wherein 2.0<n<3.0, 0.4≦x≦0.9, 0.1≦y≦0/6, and x+y=1, and n=Fe/(Co+Ni),  
       and having a particle diameter of 20 to 40 nm, a saturation magnetization σs of 50.3×10 −6  to 88.0×10 −6  Wb.m/kg and a coercive force HcJ of 279 to 637 kA/m.  
     
     
       10. Fine spinel-type ferrimagnetic particles comprising single-phase structure, comprising iron, cobalt and nickel, the ratio of an iron mole to the sum of a cobalt mole and a nickel mole being from more than 2.0 to less than 3.0, and 
       having a particle diameter of 10 to 50 nm, a saturation magnetization σs of 50.3×10 −6  to 88.0×10 −6  Wb.m/kg and a coercive force HcJ of 239 to 637 kA/m.  
     
     
       11. A process for producing fine spinel-type ferrimagnetic particles, comprising: 
       (1) mixing aqueous solutions containing Fe 3+ , Co 2+  and Ni 2+  with each other, which are prepared by dissolving each of water-soluble salts of iron, cobalt and nickel in water, at such ratio of an Fe mole to the sum of a Co mole and a Ni mole being from more than 2.0 to less than 3.0 and the Co mole to the Ni mole being 0.4 to 0.9/0.6 to 0.1,  
       (2) while stirring the resultant mixed solution, adding thereto an aqueous alkali solution in a range of from not less than one equivalent based on whole metal ion contained in the mixed solution to an amount such that the concentration of OH groups contained in a solution obtained after adding the aqueous alkali solution is not more than 3 mol/liter; and  
       (3) heating the resultant precipitated slurry at a temperature of 80 to 101° C. while stirring.  
     
     
       12. Fine spinel-type ferrimagnetic particles having a composition represented by the formula (I): 
       wherein 2.0<n<3.0, 0.4≦x≦0.9, 0.1≦y≦0/6, and x+y=1, and n=Fe/(Co+Ni),  
       produced by the process as defined in  claim 10 .  
     
     
       13. A magnetic sheet comprising fine spinel-type ferrimagnetic particles as defined in  claim 1 , and a binder resin.